It is known from prior art to make aerial cables self-supporting by using separate supporting elements. These could for example be a separate messenger wire of steel. This wire could be mounted along the cable as illustrated in the European patent EP0461794. The cable could also be twisted around the messenger wire in a spiral.
It is also known to provide cables of improved tensile strength by embedding supporting elements in the cable insulation as described in U.S. Pat. No. 4,956,523.
A disadvantage of using these supporting elements is that the cables become expensive to produce. A cable with a supporting element also becomes heavier and for steel messengers there is often a demand that the messenger wire should be grounded for safety reasons which complicates the mounting in cable fixing points.
An electrical cable comprises one or several conductors that are made out of aluminum or copper. One solution is therefore to let the conductor itself act as the supporting element.
The conductors are normally surrounded by a plurality of different layers or shields, conductor shields, insulation shields, screen etc. If the different layers and/or conductors within the cable are not adhered to each other it becomes easy to bend the cable as the layers/conductors can stretch and slip relatively each other. This slippage is however undesirable for self-supporting cables. To overcome the slippage an inwardly directed radial pressure force to the cable in the cable fixing points can be applied so that the slippage is avoided. This force needs however to be very strong and has the disadvantage of damaging the outermost layers of the cable.
A solution to avoid the slippage is to simply make the different layers/conductors adhere to each other (for example by gluing or melting). This has however the disadvantage that the cable will become difficult to bend and it will also be very difficult to separate the different layers/conductors from each other without damaging the cable when jointing or terminating.
In U.S. Pat. No. 6,288,339 layers with undulations are disclosed. This solution has the effect that the layers can slip relative each other to some extent when the cable is bent, but in response to a relatively low inwardly directed radial pressure force the undulated layers cam into each other whereby the slippage is avoided. However, the flexibility becomes somewhat limited for large dimension cables.